Our broad goals are to study the biological constrains and the role of experience in setting up functionally specialized neural systems in normal development and to study the nature and extent of changes in this process in cases of abnormal development. An important approach is to study changes in brain organization that occur as a function of chronological age and to contrast these with changes linked to specific abilities when age is held constant. The variability occurring in normal development provides on opportunity to address this issue. The study of abnormal development, as in the case of language impaired (LI) children, children with foci brain lesions (FL children) and children with Williams Syndrome, provide another opportunity to link specific changes in neural development with alterations in specific cognitive processes. To this end we will record event-related potentials (ERPs) from over several specific cognitive processes. To this end we will record event-related potential (ERPs) from over several regions making comparisons within and between the cerebral hemispheres in a series of studies designed to assess different aspects of language, spatial, and attentional processing. The specific aims are to assess the hypotheses that (a) different neural systems mediate semantic and syntactic aspects of language processing from an early age, (b) neural systems important in grammatical processing are more vulnerable to early experience than are the systems that mediate semantic processing and these may be abnormally organized in children LI, focal brain lesions, and Williams Syndrome (c) some of the patterns of abnormal brain activity linked to language processing in the clinical populations may be elicited in normal children under stressed conditions related to perceptual or temporal difficulties (d) examine the timing and organization of neural systems that mediate different aspects of visuo- spatial processing within the dorsal and ventral visual streams in children who show abnormal spatial abilities (WMS and FL with RH damage), and (d) functional organization within the right hemisphere for spatial processing may be affected by abnormal organization of neural streams in children who show abnormal spatial abilities processing within the dorsal and ventral visual streams in children who show abnormal processing with the dorsal and ventral visual streams in children who show abnormal spatial abilities (WMS and FL with RH damage), and (d) functional organization within the right hemisphere may be affected by abnormal organization within the left hemisphere in children with abnormal organization for language, LI, WMS and a subset of children with FL.